It is known that an enzyme, aromatase, takes part in the final stage of biosynthesis of estrogen. Aromatase aromatizes the ring A of the steroid and uses androgen as a substrate to produce an estrogen. Inhibition of the aromatase activity leads to prevention and treatment of various diseases in which an estrogen participates as an exacerbating factor.
Several aromatase inhibiting compounds have hitherto been proposed based on the above concept. Typical examples of known aromatase inhibiting compounds include imidazolyl-, triazolyl-, pyridyl- or pyrimidyl-substituted methyl compounds disclosed in EP-B-236940, EP-B-293978, U.S. Pat. No. 4,762,836, and J. Med. Chem., Vol. 33, p. 416 (1990).
Further, U.S. Pat. No. 4,774,251 describes that a compound having a pyridyl- or pyrazyl-substituted tertiary amino group and one or two phenyl groups, as represented by the following general formula, exhibits an aromatase inhibiting activity. ##STR2## (cf. U.S. Pat. No. 4,774,251 as to definitions of the symbols)
The compound according to the present invention is distinctly different in structure from any of the compounds found in the above-described literature in that it contains a pyrimidine ring, a pyridazine ring or a triazine ring as a basic structure.
Additionally, the compound of the present invention has been proved highly useful as it has 100 times or more the aromatase inhibiting activity of the compound disclosed in the literature.